1. Field of Invention
This invention relates to the methods of making liquid nitrogen-sulfur fertilizers for direct application to the soil. Liquid fertilizer has come into wide-spread usage in locations where irrigation rather than rainfall is predominantly used to irrigate crops, such as California. Liquids are readily introduced into the irrigation systems and do not clog pipes or valves. With the relatively recent advent of drip irrigation, the problem of clogging small diameter openings is severe.
The reaction between urea and concentrated sulfuric acid is categorized as follows: ##STR1##
The reaction is strongly exothermic and explosion may result if concentrated sulfuric acid is used without dissipating the heat. The resulting end product is a liquid which remains in the fluid state at most temperatures. This liquid fertilizer is ideally suited to the relatively new methods of drip irrigation.
2. Brief Description of the Prior Art
Previous patents teach methods of making liquid fertilizer, for example, Jones, U.S. Pat. No. 4,116,664, describes a sequential method of slowly adding sulfuric acid to powdered or prilled urea in order to control the resulting heat of the exothermic reaction. by blending in small amounts over a tortuous path through a multi-stage reactor, a liquid nitrogen -sulfur fertilizer is gradually produced. The slowness of this method is commercially impractical for producing large amounts of liquid fertilizer. Moreover, the capital investment for the reactor is substantial in relation to the volume of fertilizer produced.
Garthus, et al. U.S. Pat. No. 3,984,226 relates to a process wherein sulfuric acid reacts with ammonia gas to form a liquid. The considerable amount of equipment, i.e., holding tanks, absorbers, etc., used under this process requires substantial capital outlays. Neither of these processes of the prior art teaches the making of a liquid fertilizer by mixing urea and sulfuric acid in a quick, simple and economic batch process in which the heat of the reaction is effectively controlled.
The reaction of urea and sulfuric acid is so highly exothermic as to present a danger of explosion. Consequently, the prior processes either: (1) greatly diluted the ingredients to make a fertilizer of very low nutrient levels for the quantities packaged and shipped; or (2) very slowly prepared a concentrated fertilizer to avoid explosion. Both of these alternatives are uneconomical.